B4.002 Autonomic Nervous System Flashcards
symptoms of autonomic dysfunction
dry mouth (xerostomia) swallowing difficulty (dysphagia) airway obstruction heart rate disturbances gastric disturbances constipation or fecal incontinence erectile and/or ejaculatory dysfunction urinary retention or incontinence pupil constriction (miosis) or dilation (mydriasis) loss of sweating (anhydrosis) orthostatic (postural) hypotension / supine hypertension
what is the autonomous nervous system?
a peripheral motor system with the last inter-neuronal synapse in a peripheral ganglion
regulates involuntary movement
typical targets of the autonomic nervous system
smooth muscle
glands
heart
2 components of ANS
sympathetic nervous system
parasympathetic nervous system
how are voluntary motor pathways different from autonomic motor pathways?
voluntary don’t have neurons in ganglia
CNS neurons project directly to muscle
basic flow of autonomic signal
intermediolateral column preganglionic axon ganglion postganglionic axon target
nerves involves in PNS
cranial (3, 7, 9, 10)
sacral
targets of PNS
heart
glands
smooth muscle
nerves involved in SNS
thoracic
lumbar
targets of SNS
head
skin, muscles, glands of trunk and extremities
viscera
genitalia
what is a paravertebral chain
22 ganglia string together
SNS travels through this chain to get to targets
target can be on the same level as the CNS nerve effector or can move up or down from the effector via the paravertebral chain
what is the splanchnic nerve
part of SNS
innervates viscera and genitalia
goes through prevertebral ganglion
which ganglia have cholinergic excitatory synapses?
BOTH sympathetic and parasympathetic ganglia
what receptors mediate excitatory cholinergic synapses?
nicotinic
how are PNS and SNS outputs different?
PNS is discrete = 1:1 ratio of pregangionic/postganglionic neurons
SNS is diffuse= preganglionic neuron acts on multiple post (divergence), post ganglionic get inputs from multiple pre (convergence)
what are varicosities
segments of dilation along postganglionic axon
close to effector cells
what is a ground plexus
network/mesh of varicosities over cells of autonomic target
describe an autonomic neuroeffector junction
not technically a synapse, but similar function
axon ensheathed by Schwann cells except at varicosities
at these varicosities receptors are present to mediate communication with receptors on nearby target cells
multiple mitochondria and vesicles
2 primary types of parasympathetic transmission
ACh
NO
describe the process of ACh parasympathetic transmission
ChAT (choline acetyltransferase makes ACh)
ACh released via vesicles into junction
can act on multiple M (muscarinic) receptors on effector cell
AChE breaks down ACh quickly
choline is transported back into neuron to be recycled
M1, M3, M5
excitatory muscarinic receptors
act on smooth muscles and glands
M2, M4
inhibitory muscarinic receptors
act on smooth and cardiac muscles
describe the process of NO parasympathetic transmission
NOS makes NO
NO released from neuron
NO acts on guanylate cyclase receptor on effector cells
NO diffuses away
guanylate cyclase
inhibitory receptor
relaxes vascular smooth muscle
2 primary types of sympathetic transmission
ACh (5%)
NE (95%)
synthetic enzyme of NE
dopamine B-hydroxylase
termination of NE action
reuptake (80%)
COMT, MAO degradation enzymes (10%)
receptors for NE
adrenoreceptors
effects of ACh sympathetic transmission
eccrine sweat gland excitation
forehead, chest, face, etc
types of adrenoreceptors
a1 a2 b1 b2 b3
a1
+
smooth muscle and gland excitation (contraction/ increased salivation)
a2
-
inhibits NE release
b1
\+ cardiac excitation (increased inotrophy/ chronotrophy) renin release (increased angiotensin II)
b2
smooth muscle relaxation (-) glandular secretion (+)
b3
+
stimulated lipocyte lipolysis
which adrenoreceptor does NE not act on as much as E does
b2
which adrenoreceptors are responsive to E
all
which adrenoreceptors are responsive to isoproterenol
B only
which adrenoreceptors are responsive to phenylephrine
a1 only
decongestant
which adrenoreceptors are responsive to clonidine
a2 only
which adrenoreceptors are responsive to NE
all but b2 is weak
where are a1/a2 receptors located
a1: post junctional
a2: pre junctional
where are B1 receptors located
heart
kidney
where are b2 receptors located
smooth muscle
glands
where are b3 receptors located
fat
what is the adrenal medulla
modified sympathetic ganglion
how does the adrenal medulla regulate the body?
nerve from the CNS synapses with the adrenal medulla chromaffin cell via a cholinergic nicotinic synapse
phenylmethanolamine N-methyl transferase converts NE to E within adrenal medulla
E (80%) and NE (20%) released directly into blood stream
how do autonomic nerves regulate the amount of transmitter released?
prejunctional inhibitory autoreceptors (a2 for example)
how can postjunctional receptor sensitivity change
abundant agonist = desensitization
transmitter amts low = increased sensitivity
what does the sympatho-adrenal system do
mediated fight or flight
prepares organism for mental or physical challenges
broad and diffuse system activation
what does the parasympathetic system do
conserves and protects
discrete changes in activity of selected organs
rules of the parasympathetic system
- always activates non-vascular smooth muscle (except sphincters) - cholinergic
- always relaxes sphincters - cholinergic
- always inhibits cardiac activity (vagal) - cholinergic
- always activates glands - cholinergic
- when present, relaxes vascular smooth muscle - nitrergic
rules of the sympathetic system
- contracts smooth muscle via a1
- relaxes smooth muscle via b2
- excited heard and kidney cells by b1
- excited adipocytes via b3
- increases glandular secretion by a1, b2, M (eccrine)
discuss autonomic regulation of the pupil
sympathetic- contraction of dilator muscle, pupil diameter increase (mydriasis), eyelid retraction (bugging out eyes)
parasympathetic- contraction of constrictor muscle, pupil diameter decrease (miosis)
horners syndrome symptoms
ptosis miosis facial anhidrosis facial flushing indicators of damage to sympathetic innervation
discuss the autonomic regulation of the GI system
sympathetic- reduces motility, increases sphincter tone
parasympathetic- increases motility, decreases sphincter tone, increases enteric blood flow via dilation
discuss the autonomic regulation of the bladder
retention = not enough parasympathetic ACh incontinence = not enough sympathetic NE
discuss the autonomic control of erectile function
erectile tissues blood vessels normally constricted
with arousal, PNS axons fire and release NO
NO acts on gualylate cyclase to produce cGMP which causes smooth muscle relaxation, vasodilation, and tumescence
what is the basis of erectile dysfunction?
sacral parasympathetic nerves degenerate so NO release is insufficient
how does Viagra work?
inhibit phosphodiesterase type 5 which breaks down cGMP
amplifies effects of NO
source of dry mouth
reduces SNS/PNS excitatory innervation
source of dysphagia
reduced PNS mediated motility
source of airway obstruction
PNS constriction due to loss of SNS dilation
sources of heart rate disturbances
SNS loss = bradycardia
PNS loss = tachycardia
sources of gastric disturbances
PNS loss = hypomotility
SNS loss = hypermotility
sources of constipation/fecal incontinence
PNS loss = constipation
SNS loss = incontinence
sources of erectile/ ejaculatory dysfunction
PNS loss = erectile
SNS loss = ejaculatory
sources of urinary retention or incontinence
PNS loss = retention
SNS loss = incontinence
sources of pupil constriction/dilation dysfunction
PNS loss = dilation
SNS loss = constriction
source of loss of sweating
loss of SNS cholinergic
